Modified sweep circuit



May 11, 1948. I w. A. MiLLER ETAL 2,441,246

' V MODIFIED SWEEP CIRCUIT Filed Nov. 2, 1945 I INVENTORS A 0 1 #iumvvfi4/41/54. war K UUE I I Z g qa/ A JP/i/v fi: V2 WW 7' a M ATTORNEYPatented May 11, 1948 2,441,245 MODIFIED SWEEP cracurr William A.Miller, Port J efierson, and Eugene It.

Shenk, Brooklyn, N. Y., assignors to Radio Corporation of America, acorporation of Delaware Application November 2, 1943, Serial No. 508,702

The present invention relates generally to a method of and means forgenerating saw-tooth voltage waves. Circuits for generating saw-toothvoltage waves are generally referred to as sweep circuits because of thefact that the saw-tooth 5 saw-tooth voltage wave obtained from thecirvoltage wave is utilized to vary the voltage on cuit of theinvention. The ordinate represents the horizontal deflection plates of acathode ray voltage while the abscissa represents time. It isoscilloscope, as a result of which an electron desired that thesaw-tooth voltage wave increase beam sweeps" or scans the fluorescentscreen linearly from a normal value to a particular on the oscilloscope.point D at which it is desired that the voltage More specifically, thepresent invention proof the saw-tooth wave remain at rest for an invidesa method of and a circuit arrangement for terval T from D to F, afterwhich the voltage modifying the normally linear sweep or sawwave-formshould again increase linearly from tooth voltage wave-form in suchmanner that the point F to point G with the same slope that it hadvoltage wave increases linearly to a particular between the point oforigin and point D. It point or voltage value, then remains stationaryshould be noted that at point D the voltage of at this point or voltagevalue for a predetermined the saw-tooth wave increases rapidly by avalue interval of time, and then increases again linear- M, then remainsat rest for a period T until the ly for the normal duration of thesaw-tooth voltpoint F is reached, after which the normally age wave. Thepresent invention permits an linear increase in voltage of the saw-toothwave adjustment of the particular point or Voltage is continued. Itshould be noted that the overall value of the saw-tooth voltagewave-form t linear increase in voltage of the saw-tooth wave 1 which theincrease in voltage is stopped for the from e po n of Origin 110 PointGgis the Same desired period of time. as would occur without themodification pro- Although it is known in the prior art to modid -Ced bythe sudden increase in voltage at point fy the wave-form of a normallylinear saw-tooth D and. the rest in the interval T. Before P generator,such known circuits hav modified th ceeding with a discussion of thecircuit of Figsaw-tooth wave-form at the expense of a net in- 1116 2, itShould. at this time be noted that the crease or decrease of the finalsaw-tooth voltage, time T at which the voltage of the saw-tooth or havecaused a change in the slope of that por- 30 Wave remains at re tcorresponds in m i tion of the saw-tooth wave which follows the durationto the rectangular pulse'shown n line modified portion. By means of thepresent in- Z of Figure 2. It should also at this time be vention,however, we are able to produce a sawnoted that the time interval of thesaw-tooth tooth wave which normally increases in value at voltage wavebe w the P in f orl ln and a constant rate, and then stops increasing in35 the Doiht G is qu 13 t e du at on of the me voltage value at somepoint in the saw-tooth tive pulse shown in line Y. The reasonior thiswave for a, desired interval of time, after which 13 described ingreater detail in 00111180131911 Wlth the saw-tooth voltage wave-formcontinues northe operation of the circuit diagram of Figure mally toincrease with the same slope as before Referring to Figure 1,'there areshown a pair the stoppage 0f the wooth voltage wave. 40 ofvacuum'tubesvl and V2 having their cathodes Moreover, by means of thepresent invention, the directly connected together and 1n circuit with achange in the saw-tooth voltage wave does not common cathode resistorR5. The o tube aifect either the duration or the amplitude of Vi isconnected directly to f Its PQ the overall saw-tooth voltage wavePutting it is connected to a source of pos1t1ve polarizing in otherwords, the end result of the modified potential EB. The rid of e V2 15connected saw-tooth voltage wave produced by the present through. a pairof resistors R6 and R1 to the invention insofar as duration or amplitudeis concathode of the same tube. The junction P011117 cerned is the sameas the saw-tooth voltage wave of the resistors R6 and R1 is connected.to terwould have been without the modification. minal A to which theinput pulse of line Z of A more detailed description of the invention 0Figure 2 is applied. The anode o tube 15 follows in conjunction with adrawing, wherein: connected through an adjustable resistor R2 to 7Figure 1 illustrates, by way of example only, a-positive source EB.Between the anodes of the one circuit embodiment of the presentinvention two tubes VI and V2 there are provided "a res for producing amodified saw-tooth voltage wave R4, a pair of. diode V4 and V5, and aconde s having the above mentioned characteristics, and Cl, as shown.Another diode V6 is connected 4 Claims. (01. 250- 27) Figure 2graphically illustrates the operation of the present invention by meansof a series of curves X, Y and Z.

Graph X of Figure 2 illustrates the type of between ground and theJunction point between diode V and condenser Cl. A third vacuum tube V3having a resistor R3 between its grid and cathode and a condenser C2between its anode and cathode is connected from a point between the twodiodes V4 and V5 to another source of positive potential +E. Thepositive voltage obtainable'from source +E is less .th'an that obtainable from source"+Ee. The grid of-tubeV3 is connected through acondenser to terminal B to which a negative rectangular wave pulsegeneral-L ly of the form of graph Y of Figure 2.is.supp lied.

The operation of the circuit of Figure lin its three essential steps inthe operationriot-the-zcom-iplete cycle will now be describedziSt'artingvwith; the quiescent condition before: the application of anypulse to either terminalsA Or-B, the-vacuum tube Vi will benon-conducting while the vacuum tubes V2 and V3 will be conducting;

the second essential step in the cycle of operations; with the'applicationiot-z a: negative :rectangular wave pulse-Yrto terminal Bthe-vacuum tube V! will still be non-conducting, the.vacuum tube V2will. still be conducting; while the-vacuum tube V3' will be.- irrthe.non conducting gcondition because of the applicationrcf i asnegativeinput pulse to. its grid: Mathexthirdessentialstep'of the:cycle' of operations; with thenegative-rectangular-wave :pulse .Y still:applied :to terminal B and with the negative rectangular wave inputpulse 2 .applied to terminal. -A-,- theevacuumetube VI will becomeconducting; while.-. the vacuum tubes V2 and V3 will be.non-iconducting; The vacuum tube-V3 .will remain non-conducting untilthe end "of the rectangular wave-pulse .Y applied to terminal B;

Considering thezoperatioir of Figured .inmore detail, withparticular-reference to the :various circuit elements,: the vacuum tube.V-l will be.non-. conducting and thervacuumtubes V2:and vawin beconducting'during the quiescent condition-,- that' is; prior" to';the-application. of" negative pulses, toi either: of the; terminals; A:and: B. In this. quiescent: condition; it; will be: seen that thee grid:of: tube: V2? has no bias. applied thereto; as aresultiiottwhichrcurrentwill-iiow from the positive: source;+EB;throug-hresistor R2 and through the vacuum tube VZEtoground through thecommon'zbias resistorR'o'. The :flow of current through: resistorz R5"will produce an IR drop therein which applies :suifi'cient negative biasto the gridoftubeVl -to :cut-ofi-thefiow of anode current in thisrtube;Inasmuch-as; the negative rectangular wave .pulsehasnot .beenapplied toterminal B in thiszquiescent condition of operation, there will bernmbias onathezgrid'of tube V3 andthis tube wi'llialso'- be conducting.As aresult of the status: of.these'sthree-.-tubes, in this particularconditiomof: operation; there willbe a fiow ofcurrentfromrtheapositive.source +-Ee through resistors: RI: and; R4=- in:series, through di'ode V4 and throughzvacuumtube- V3 to the source- +E.Source =E'Zastbefore mentioned, has a-positive valuelessF than that ofsource-EB. As a result of'th'is; a charge; will build. up on condenserC2,- but this'chargeWilLbe oii small value dueto the factthat thesvalueof resistors RI and R4 taken togetherrisilargezcompared to the -internalimpedance f: the-pvacuum tube V3. This residual charge will always. beon the conidenser C2 and is. indicated. by. thesmall positive amount'on' the ordinateeabove the reference: line 0' in graphiX of: Figure-2.-This .ordinate: represents the voltage. on. the condenser C2; and. islabeled 'Eca- It 'wilLthus-beenseen.thatthe saw:-

tooth sweep voltage starts with a small positive potential. In the nextessential step in the operation representing the condition with only thenegative pulse applied to terminal B (note graph Y of Figure 2), thisnegative pulse will bias the tube V3 to anode current cut-ofi, as aresult of which the charge on condenser C2 will start to buildup'li-nearly'."

Inthisrstep in the cycle of operation, tube V2 is still conducting andtube VI non-conducting. At some later time, when it is desired to stop.the increase in voltage on the condenser C2, for-a desired period oftime, representing the third essential step in the cycle of operation ofFigured;there-isapplied to terminal A a negativeinputpulse'of amagnitude sufficient to cut off the flow of anode current through tubeV2. (Note graph Z'of Figure 2.) The application of a negative inputpulse to terminal A causes the tube V2 to be non-conducting as a resultof which the flow of current through R5 produced by the current flow intube V2 :ceases, thus per,- mitting tube V! to conduct. Si-nce thenegative input pulse applied to terminal-B ,-is,.of longer duration.than: that applied toterminal A it-will. be seen that in thisparticularstep. in-the-cycle of op erations, tub es. V2 -.and- V3 arenon-conduct.- ing while tubeVl :is conducting... Undenthis condition ofoperation, .in which .tube Vl. is. conducts ing, there will be a flow ofcurrent;thr,ough-v re: sistor RI,- in. .turn causing .a;decreaseinthevoltage applied. to the anode :of diode. V4 throughresistor. R4. Thevoltage now availableonihe anode of diode. V4 .is..less.p,ositive .than .the volt-lage on the cathode .oi. the. same, ,diodapasare.- sult of which thediode. V4 will..cease.conduct-. ing, thusstoppingthe. building- .up...of.ithe char e on the condenser. 0.2.;over.the. path. which. in.- cluded the diode Va and .resistorsRA and; Rliinseries- At .the. same .time that diode vfceased conducting, there .will.be. a sudden rise .in. the potential of the charge oncondensencfreprsented by the. amount LMJin graph .Xilof Figu e 2. due to the fact thatwhentubeVZ'ceasescouducting there. is a. rise: in. potential applied; tothe circuitincluding resistor R2; condenser; G! dicdevfi and.condenserCZLinseries. This risein potential makes diode. V5. conduct.andjcharses condensers. C2 1 and 01 in, .series. Condenser C2willremain charged, to thesuddenly. increased amount represented bypointDin graph X-oi Fig.1 ure 2,. for thetimecinterval-T correspondingto the.duration, of the. negative input pulse applied to terminal ,A. (note.Figure. 2.) When the neg! ative input .pulse. applied to.v terminal .A..ceases, vacuum. tube V2; will again. conduct. and, bias vac-um tube VI.to -the. noneconducting state.

During. the time interval of the. negative. input pulse Z applied toterminal.A-,.it will .benotedthat the charge onv condenser 02. remains.constant. as represented by the horizontal line betweenpoints D and F ongraph Xof Figure .2. The .-fiow otcurrent through V2. after thetermination of, the negative input pulse. applied. to terminal A willnow reduce thevoltage available in .the path .in: cluding R2, Cl anddiode Veto a-positivevalue less than. the value, of source..+E,asaresultof which, the a diode V5 will cease conducting. and condenserCi. will discharge through. diode. V6. The time required for. thesuddenincrease-.in voltage on condenser CZduring the time-interval when diode-V5 is conducting depends upon the time constantof thecircuit includingresistor.R;2 and condensers Cl .and 02 while the amount of suddenincrease in voltage on condenser G2: de-

pends upon the ratio of O2 to CI and upon the value of R2 When diode V5becomes non-con ducting, simultaneously therewith diode V4 becomesconducting to reestablish a charging path for condenser C2 through diodeV4 and resistors R4 and RI in series. The reestablishment of this chargepath for condenser C2 causes the charge on condenser C2 to increaselinearly from point F to the end of the cycle of operations representedby point G in Figure 2. It should be noted that except for the timeinterval T, the saw-tooth grave is linear and represented by a singlestraight In the design of the circuit of Figure 1, the time constantsand values of the various elements are such that the height M of Figure2 representing the sudden increase in voltage on C2 atpoint D and therest period T during which the charge on condenser 02 remains constantare in the same ratio as the height of the saw-tooth wave at time G andthe duration of the complete saw-tooth wave represented by the time ofthe negative input pulse on graph Y.

It will" be noted that the time T during which the saw-tooth wave ismodified and during which the charge on condenser C2 remains constantdepends upon the position of the negative pulse Z supplied to terminal Aand its duration. By moving the position of the pulse applied toterminal A, we can thus modify the saw-tooth wave at any desired pointin its cycle in accordance with graph X of Figure 2.

One use of the present invention, given by way of example only, is inconnection with a radio locating and detecting system employing antennalobe switching. In such a system, pulses of radio frequency energy aresent out in all four quadrants of a circle and it is important todistinguish on the oscilloscopes between pulses received during thedifferent quadrants of the lobe switcher. By means of the presentinvention, one is able effectively to displace on the oscilloscope onereceived pulse with respect to another received pulse in an oppositequadrant. For an example of an antenna lobe switching system of theprior art, reference is made to Lindenblad application, Serial No.454,661, filed August 13, 1942, and to Miller copending application,Serial No. 473,801, filed January 28, 1943, U. S. Patent 2,422,361,issued June 1'7, 1947.

What is claimed is:

1. The method of generating a modified sawtooth wave by means of acircuit including a condenser, which eomprises linearly charging saidcondenser to a desired point in the charge cycle, suddenly increasingthe charge on said condenser by a desired amount, maintaining constantthe charge on said condenser for a predetermined interval of time afterthe sudden increase of the charge, and then again linearly charging saidcondenser at the same rate as before.

2. The method of generating a modified sawtooth wave by means of acircuit including a condenser, which comprises linearly charging saidcondenser to a desired point in the charge cycle, suddenly increasingthe charge on said condenser by a desired amount, maintaining constantthe charge on said condenser for a predetermined interval of time afterthe sudden increase of the charge, and then again linearly charging saidcondenser at the same rate as before, the ratio which the amount of saidsudden increase in charge on said condenser bears to said predeterminedtime interval being the same as the ratio which the total maximum chargeon said condenser bears tothe total time it takes for said condenser toreach said maximum charge.

3. A generator of modified saw-tooth waves comprising first and secondvacuum tubes each having a cathode, a grid and an anode, a directconnection between the cathodes of said two tubes, a common cathoderesistor for said two tubes one terminal thereof being grounded,separate resistive connections from the anodes of said two tubes to asource of positive undirectional polarizing potential, a connectionfrom-the grid of said first tubeto ground, a resistive connection fromthe grid of said second tube to its cathode, whereby said second tubenormally draws current and biases said first tube to anode currentcut-01f, a circuit between the anodes of said two tubes, a condenserconnected between said circuit and a second source of positiveunidirectional potential, the positive potential of said lastsource'being smaller in magnitude than the positive potential of saidfirst source, a vacuum tube shunting said condenser, a connection forsupplying to said vacuum tube a negative pulse of suilicient magnitudeto render said last vacuum tube nonconducting, to thereby enable acharge to build up on said condenser over a circuit including the anoderesistive connection of said first tube, and a circuit for supplying anegative pulse to thegrid of said second tube of a duration less thanthat of said other negative pulse and of a magnitude suflicient to biassaid second tube to cut-off, as a result of which said first tubebecomes conducting for the interval of said smaller duration negativepulse, and the shape of the saw-tooth wave produced by 'said generatoris modified.

4. A generator of modified saw-tooth waves comprising first and secondvacuum tubes each having a cathode, a grid and an anode, a directconnection between the cathodes of said two tubes, a common cathoderesistor for said two tubes one terminal thereof being grounded,separate resistive connections from the anodes of said two tubes to asource of positive unidirectional polarizing potential, a connectionfrom the grid of said first tube to ground, a resistive connection fromthe grid of said second tube to its cathode, whereby said second tubenormally draws current and biases said first tube to anode currentcut-ofi', a circuit between the anodes of said two tubes, comprising theseries connection of a resistor, a first diode, a second diode and afirst condenser, said first resistor of said series connection beingdirectly connected to the anode of said first tube, while said firstcondenser is directly connected to the anode of said second tube, thecathodes of said two diodes being directly connected together, a thirddiode connected between ground and the junction point of said seconddiode and first condenser, a second condenser connected from thecathodes of said first and second diodes to a second source of positiveunidirectional potential, the positive potential of said last sourcebeing smaller in magnitude than the-positive potential of said firstsource, a third vacuum tube having its anode connected to one terminalof said last condenser and its cathode connected to the other terminalthereof, a connection for supplying to the grid of said last vacuum tubea negative pulse of suificient magnitude to bias the tube to anodecurrent cut-off for the duration of the pulse to thereby enable a chargeto build up on said second condenser over a path including the anoderesistive connection of said first tube and the resistor and first diodeof said series connection, and a circuit for supplyal -negative pulsewtoine gnidsof said: second tube ofeawduration lesethan that of said otherpulse end-eta magnitude sumcient to bias said second tube to. cut-off,as a result of which said firststube beoomes'oondueting andzproduces-anlR drop imitswanode oircuitof sumcient value as to interrupt theehargingpath fer-said second condenser fer :the intewal ofesaid-smallerduration negabiveepulse, saidsecond -condenser having its changesuddenly increased when-said charging 10 path :is-interrupted,ever a,pathincluding the second-diode, thefiflrst condenser and the anoderesistive connection of said second tube; after which the 'ohaf-rgeon-the second condenser remainsoonstant :for the: time during. whichsaid second. tube is out off, said second tube again drawing 'ourrentupon the termination of said smaller duratimi-negative pulse, as aresult of which saidlfirst tube becomesnon-conduoting and the charge onsaidsec'onw condenser again builds up to a ts-maximum value, thetermination of said 8 longer duratiom negative ipulse' permittingsaidth-ird tube to draw current and 'dischargeseidsecondmondenser.

WILLIAM-A. EUGENE R; REFERENCES CITED The following references are ofrecordm me file of this I patent:

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